Powertrain control system for a vehicle utilizing vehicle acceleration

ABSTRACT

A method for monitoring an electronically controlled drive unit of a vehicle uses actual vehicle acceleration and a preselected vehicle acceleration. Actual acceleration is determined from any of an acceleration sensor or vehicle speed sensors. When actual acceleration is greater than the preselected acceleration, a reaction is initiated to reduce vehicle acceleration. A method for controlling vehicle acceleration is also disclosed where desired acceleration is determine from either the operator command or a cruise control system.

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/532,685, filed May 21, 2000 entitled, “MONITOR FOR VEHICLE”.This application hereby explicitly incorporates by reference the entirecontents of U.S. patent application Ser. No. 09/532,685.

FIELD OF THE INVENTION

The field of the invention relates to monitoring of electronicallycontrolled drive units in vehicles.

BACKGROUND OF THE INVENTION

In some engines, an electronically controlled throttle is used forimproved performance. In addition, engines also may be controlled usingengine output, or torque control where the actual engine torque iscontrolled to a desired engine torque through an output adjustingdevice, such as with the electronic throttle, ignition timing, air-fuelratio, or various other devices.

In the electronic throttle control system, it is desirable toincorporate various features, such as cruise control and tractioncontrol. On approach for providing this type of integrated controlsystem is described in U.S. Pat. No. 5,400,865. In this system, adesired torque is calculated that provides constant vehicle speedrunning. Also, a desired torque is calculated that prevents wheelslippage. Finally, a desired torque is calculated that is requested bythe operator. A maximum of the driver requested torque and cruisecontrol torque is first selected, and then the minimum of this resultand the traction control torque is selected as the final desired torque.Then, the vehicle's powertrain is controlled to provide the finallyselected torque.

The inventors herein have recognized a disadvantage of the aboveapproach. In particular, with prior art torque arbitration schemes, themaximum of driver demanded torque and cruise control torque wasselected. However, if negative torque is needed to control vehicle speedduring cruise operation, such as down a hill, such control is notavailable since zero torque is typically the minimum torque allowed whenthe driver is not actuating the pedal. Alternatively, If negativetorques are used in the driver demand table, then tip-out performance,or foot off pedal performance, and coasting driveability are sacrificedon level roads. Driveability is Oacrificed in level roads since thenegative torque requests may cause downshifts on some tip-outs. Suchtransmission shifting can degrade drive feel on level roads.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a monitoring approachfor use with vehicles having a single or multiple power sources.

The above object is achieved and disadvantages of prior approachesovercome by a method for controlling a powertrain of a vehicle,comprising: determining a first desired vehicle acceleration based on adriver command; determining a second desired vehicle acceleration basedon a speed control strategy; selecting one of said first desired vehicleacceleration and said second desired vehicle acceleration; andcontrolling the powertrain so that an actual vehicle accelerationapproaches said desired vehicle acceleration.

By selecting between different desired vehicle accelerations, consistentdrive feel is provided on level roads, as well as on gradients, with asingle architecture and calibration. In particular, with the claimedstructure, it is possible to use a single set of calibration values onboth level and hilly roads, and achieve consistent vehicle performance.Further, it is possible to control vehicle speed on a downgrade byproviding the requested negative torque while cruise control is bothengaged and digengaged. In other words, the driver will have improveddeceleration control on both level roads and gradients.

An advantage of the above aspect of the present invention is a potentialfor reduced system complexity and/or cost.

Another object of the present invention is to provide improveddriveability both during cruise control and noral driving.

BRIEF DESCRIPTION OF THE DRAWINGS

The object and advantages of the invention claimed herein will be morereadily understood by reading an example of an embodiment in which theinvention is used to advantage with reference to the following drawingswherein:

FIG. 1 is a block diagram of a vehicle illustrating various componentsrelated to the present invention;

FIGS. 2-6 are block diagrams of embodiments in which the invention isused to advantage; and

FIG. 7 is a block diagram illustrating an alternative embodiment of thepresent invention.

DESCRIPTION OF THE INVENTION

Referring to FIG. 1, internal combustion engine 10 and motor 11 of avehicle (not shown) are shown coupled to transmission 14. Engine 10 andmotor 11 can be coupled in various ways known to those skilled in theart, such, for Example, in a parallel fashion, a series fashion, or anycombination thereof. Motor 11 can be an electric motor capable ofsupplying power to or receiving power from transmission 14. For example,motor 11 can be used to provide regenerative braking or to provide thevehicle tractive force from batteries (not shown) that store energy.Transmission 14 is coupled to a first set of drive wheels 20. Inaddition, to provide all wheel drive, transmission 14 can also becoupled to a second set of drive wheels 22. Transmission 14 can be acombined gear set and torque converter, a continuously variabletransmission, or any other power transfer unit known to those skilled inthe art and suggested by this disclosure.

Continuing with FIG. 1, accelerator pedal 40 is shown communicating withthe driver's foot 42. Accelerator pedal position (PP) is measured bypedal position sensor 134 and sent to controller 12. Also, brake pedal44 is shown with brake pedal sensor 46 providing brake signal (BS) tocontroller 12.

Controller 12 receives various signals from sensors coupled to engine10, motor 11, and the vehicle, in addition to those signals previouslydiscussed, including: first measurement of vehicle speed (VS1) of wheel20 from sensor 30, second measurement of vehicle speed (VS2) of wheel 22from sensor 32, measurement of vehicle acceleration (SIGNALL) fromaccelerometer 50, and various other signals from sensors 52. These othersignals include engine coolant temperature (ECT), and air chargetemperature (ACT). Also, controller 12 sends signals to actuators 70.

Accelerometer 50 can also be coupled to airbag system 60. Thus,according to the present invention, a single sensor can be used for bothan airbag system and a vehicle monitoring system. In addition,accelerometer 50 is capable of outputting a signal representative ofvehicle acceleration at all vehicle speeds, including zero vehiclespeed. In other words, determining vehicle acceleration from a vehiclespeed sensor may provide degraded performance at low vehicle speeds.This is because the pickup, sometimes magnetic, which generates a signalwhen a certain point of the vehicle wheel rotates past the pickup. Ifthe vehicle wheel is not rotating, no signal is produced anddeterminations of vehicle speed and/or vehicle acceleration aredegraded. However, the accelerometer is capable of outputting a signalindependent of vehicle speed, and thus the present invention can monitoreven at low vehicle speed.

In the embodiment described herein, controller 12 is a conventionalmicrocomputer including: microprocessor unit 102, input/output ports104, electronic memory chip 106, which is an electronically programmablememory in this particular example, random access memory 108, and aconventional data bus.

In the embodiment described herein, engine 10 is electronicallycontrolled by an electronic throttle control system (not shown). In sucha system, the drive unit, which in this cage is engine 10, motor 11, andtransmission 14, is controlled to produce a desired vehicleacceleration. Such an acceleration control system is described laterherein with particular reference to FIGS. 4-6. Also, controller 12provides a speed control function wherein vehicle speed is controlled toa desired speed set by the vehicle driver.

Referring now to FIG. 2, a routine is described for monitoring theelectronically controlled drive units in the vehicle. First, in step200, a determination is made as to whether speed control is active. Whenthe answer to step 200 is NO, the routine continues to step 210. In step210, desired acceleration (desrate, or acc_dd_req) is determined basedin part on a function (f1) of pedal position (PP) and vehicle speed(VS1) as described later herein. In an alternative embodiment, desiredacceleration (desrate, or acc_dd_req) can also be adjusted based onactuation of the drake pedal. In addition, in still another embodiment,desired acceleration (desrate, or acc_dd_req) can also be adjusted basedon the position of a gear selector. For example, in automatictransmissions, the level that selects P,R,N,D,L,1 (park, reverse,neutral, drive, low, low 1, etc.) is taken into account in determiningdesired acceleration. In still another embodiment, desired accelerationcan be modified depending on whether a switch is set to a “sport” modeor a “fuel economy” mode. Then, in step 220, actual vehicle acceleration(actualrate) is determined as described later herein with particularreference to FIG. 3.

Continuing with FIG. 2, in step 230, a determination is made as towhether actual acceleration (actualrate) is greater than the desiredacceleration plus a first calibratable threshold (T1). When the answerto step 230 is NO, timer is reset to zero in step 240. Otherwise, timeris inctemented by the computer loop time (looptime) in step 250. Next,in step 260, a determination is made as to whether actual acceleration(actualrate) is greater than the desired acceleration plus a secondcalibratable threshold (T2) or timer is greater than third calibratablethreshold (T3). In one embodiment, threshold T2 is greater thanthreshold T1.

When the answer to step 260 is YES, a reaction is initiated in step 270.This reaction is in a preferable embodiment, decreasing engine torque.Engine torque can be decreased in a variety of methods, includingdecreasing fuel amount, decreasing air amount, retarding ignitiontiming, deactivating cylinders, or any other method known to thoseskilled in the art in view of this disclosure to reduce engine torque.Also, a reaction can be changing a transmission gear ratio to produceless wheel torque or engaging ancillary devices to consume enginetorque. Further, a reaction may be to reduce motor torque or cause motor11 to act as a generator, thereby absorbing energy and reducing wheeltorque. Further still, a reaction may be to reduce vehicle accelerationby any method listed above herein.

Referring now to FIG. 3, a routine is described for determining actualvehicle acceleration. First, in step 310, the routine determines a firsttemporary acceleration (temprate1) based on acceleration sensor 50.Then, in step 320, the routine determining second temporary acceleration(temprate2) based on first vehicle speed signal (VS1). In particular, aderivative of vehicle speed is used. In one embodiment, a lead lagfilter is used to approximate a derivative and also reduce noise. Then,in step 330, the routine determines a third temporary acceleration(temprate3) based on second vehicle speed signal (VS2). Again, a leadlag filter can be used to approximate a derivative and also reducenoise. Finally, in step 340, actual acceleration (actualrate) used formonitoring is determined based on a maximum of the first through thirdtemporary accelerations.

In the above embodiment, all three acceleration measurements are used.In alternative embodiments, various combination of these can be used,such as, for example, the maximum of temprate1 and temprate2. Also, asingle measurement alone can be used.

Referring now to FIG. 4, a control system is described for controllingthe engine and electronic throttle. Desired acceleration from thedriver, or driver demanded acceleration (acc_dd_req), is determinedbased on pedal position (PP) brake signal (BS), which can provide adesired deceleration or a deceleration brake force, and vehicle speed(VS), with modifications for barometric pressure (BP) and engine and airtemperatures (ECT, ACT) in block 410. Then, the difference betweendriver demanded acceleration and “droop” control output (accl_droop) iscompared with desired acceleration from speed control (accl_spd_req). Inparticular, a maximum of these two values is determined as a arbitrateddesired acceleration (accl_arb _req) from block 412. “Droop” control isdescribed later herein with particular reference to 23, FIG. 5. Also,desired acceleration from speed control (accl_spd_req) is determinedbased on a vehicle speed error between a set speed and an actual vehiclespeed. In one embodiment, the vehicle speed error is used in conjunctionwith a nonlinear gain function to produce (accl_spd_req). For example,when speed error is between first and second speed error limits,accl_spd_req is linearly related to speed error. The speed error limitsmay be, plus and minus 3 MPH, for example. Outside these speed errorlimits, desired acceleration may be limited to a fixed value, such as1.5 MPH/sec, for example.

Then, this first arbitrated acceleration, accl_arb_req, and vehiclespeed (VS) are used to control vehicle acceleration in block 414 asdescribed with particular reference to FIG. 6. The output of theacceleration control is a desired wheel torque value (tqw_arb_req) and aclosed loop control torque (tqw_arb_cl).

Continuing with FIG. 4, a desired wheel torque from traction control(trc_tqw_req), a desired wheel torque from vehicle speed limiting(vslim_tqw_req), and acceleration control desired wheel torque(tqw_arb_req) are compared in block 416. In particular, desired wheeltorque from traction control is a desired wheel torque to prevent wheelslippage while desired wheel torque from vehicle speed limiting is adesired wheel torque to prevent vehicle speed (VS) from exceeding alimit value. The output of block 416 (tqw_arb_lim), which is the minimumof trc_tqw_req, vslim_tqw_req, and tqw_arb_req, is then converted toengine torque via the effective gear ratio (including torque convertermultiplication) in block 417 to produce (tqe_arb_lim). Next, a maximumallowed torque acceptable from transmission 14 (tae_lim_tran), a desiredengine torque from engine speed limiting (tqe_lim_rpm), and tqe_arb_limare fed to block 418. Further, tqw_arb_req (after being converted byeffective gear ratio into engine torque) is fed to block 418. The outputof block 418, the requested engine brake torque (tqe_brk_req), is theminimum of the inputs to block 418. This requested engine brake torque(tqe_brk_req) is then converted to a desired airflow (tqe_des_am) inblock 420 and a desired torque ratio (tr_desired) in block 422. Inparticular, when the desired engine brake torque is less than the enginebrake torque at closed throttle and normal operating conditions, atorque ratio is calculated by dividing desired engine torque by enginebrake torque at closed throttle and normal operating conditions. Then,the desired airflow is used to control the electronic throttle usingmethods known to those skilled in the art in view of this disclosure.

Referring now to FIG. 5, droop control is described. Closed loop controltorque (tqw_arb_cl) is multiplied by first gain K1 in block 510 and bysecond gain K2 in block 512, where R2 represents vehicle mass and wheeldiameter. In an alternative embodiment, gain K1 is a function of speederror and saturates outside a linear region. Also, this function can bedifferent depending on the sign of the error to give expected drive feelboth up and down hills. Then, the output of blocks 510 and 512 aremultiplied in block 514. The output is accl_droop, whose use isdescribed above herein.

Referring now acceleration control to FIG. 6, arbitrated desiredacceleration (accl_arb_req) is fed to a low pass filter with firstfilter coefficient (t1) in block 610. Also, vehicle speed (VS) is fed toa filter representing an approximate derivative with second and thirdfilter coefficients (t2, t3) in block 612. The output of blocks 610 and612 are fed to select block 614. Select block 614 selects one of the twoinputs. In particular, select block 614 prevents integrator wind up byproviding zero error when integrator output reaches a preselected value,or when the desired acceleration is arbitrated out later on in thecontrol system, such as, for example, based on some other controlsystem. The output of block 614 is fed to block 616, which represents anintegrator. The difference between the output of block 614 and vehicleSpend (VS) represents closed loop control torque (tqw_arb_cl). This isthen added to feedforward control torque (tqw_arb_ff) and producestqw_arb_req. Feedforward control torque (tqw_arb_ff) is determined froma table based on arbitrated desired acceleration (accl_arb_req) andvehicle speed (VS) in block 618. In an alternative embodiment, this canbe calculated based on vehicle mass, wheel diameter, and running losses.

Summarizing FIGS. 4-6, pedal position (PP) and vehicle speed (VS) areused to look-up a value of intended vehicle acceleration. The table isstructured with pedal position (PP) in rows and vehicle speed (VS) incolumns. It is calibrated, first, by placing an acceleration value of 0at each intersection of pedal position and vehicle speed where steadystate operation is desired. Increasingly positive values of accelerationwould be added upward and decreasingly negative values downward for eachcolumn to obtain the desired throttle tip-in feel at that speed. Asmoothing operation should be done across each row to assure smoothconvergence onto the steady state speed under constant pedal positioninput. The output of thin table is modified with multipliers forbarometric pressure and operating temperature.

The resulting driver demand requested acceleration modified to simulatedroop is arbitrated against an acceleration request from vehicle speedcontrol. The arbitration is based on the maximum of the two requesters.If vehicle speed control is not active, a sufficiently large negativerequest is issued to prevent it from interfering with the driver demand.If vehicle speed control is active and the driver attempts to overridethe system with the pedal, this will be done once the pedal inputproduces an acceleration that exceeds that of the speed control. Vehiclespeed control will automatically be limited to maximum positive andnegative accelerations specified in the driver demand tables.

Acceleration control is responsible for converting desired accelerationinto a wheel torque request and consists of the following sub-tasks:

A feed-forward term represents the driver demand or speed controlresponse to acceleration input for nominal level road conditions. Itoperates by converting the requested acceleration and current vehiclespeed into a wheel torque by using conversions based on vehicle mass andrunning loss coefficients, respectively. Because no integration orfiltering is involved, the response to input is immediate.

A closed-loop term is calculated by first integrating desiredacceleration into a target vehicle speed. The error between this targetspeed and actual vehicle speed multiplied by a gain and becomes theclosed-loop term. Because the feed-forward term responds immediatelywith a level road response, any deviation between target and actualspeeds is due to road and/or vehicle load variations. If the vehicle isoperating under nominal mass and running losses on a level road, thisterm will be zero.

A simulated droop (droop control) is achieved by taking the closed-loopterm and feeding it backward through the vehicle mass term used in theFeed-forward Term. This resulting droop acceleration term is thensubtracted from the driver demanded value of desired acceleration beforeit feeds into the speed control arbitration scheme. This wouldessentially negate the action of the Closed-loop Term, so this droopacceleration term is multiplied by a calibration coefficient thatspecifies how much compensation is desired for specific conditions (K1).A value of 0 would indicate no droop and the system would providefull-time speed control under driver demand. A value of 1 would indicatefull droop and the system would provide no closed loop compensation. Inone embodiment, a value of 0 would be used for downhill conditions andapproximately 0.5 for uphill. This would provide full compensationdownhill while restricting the amount of droop on an uphill to half whatit normally would be.

An advantage of the above structure is that a monitoring structure isprovided that is applicable to many different drive unit configurationssince the end result of vehicle acceleration is used. Further, since thearbitration between cruise control and driver demand uses acceleration,disadvantages of torque arbitration schemes are overcome. In particular,with prior art torque arbitration schemes, the maximum of driverdemanded torque and cruise control torque was selected. However, ifnegative torque is needed to control vehicle speed during cruiseoperation, such as down a hill, such control is not available since zerotorque is typically the minimum torque allowed when the driver is notactuating the pedal. Alternatively, If negative torques are used in thedriver demand table, then tip-out performance, or foot off pedalperformance, and coasting driveability are sacrificed on level roads.Driveability is sacrificed in level roads since the negative torquerequests may cause downshifts on some tip-outs. Such transmissionshifting can degrade drive feel on level roads. The prior art torquearbitration approach does not suggest how to resolve this conflict.

In the above described embodiment, acceleration control and monitoringare both within a single microprocesor 12, An alternative embodiment isdescribed in FIG. 7, where acceleration control is conducted incontroller 1 and acceleration monitoring is conducted in controller 2.In such an approach, the routines described in FIGS. 2-3 would beperformed in controller 2 while the control described in FIGS. 4-6 wouldbe performed in controller 1.

Although several examples of embodiments which practice the inventionhave been described herein, there are numerous other examples whichcould also be described. For example, the invention can also be usedwith hybrid electric vehicles using lean operating engines, or with anycombination of motors and engines that combine into a drive unit. Also,the acceleration controller can have different gains on speed errordepending if during cruise control or during operator control. Theinvention is therefore to be defined only in accordance with thefollowing claims.

What is claimed is:
 1. A method for controlling a powertrain of avehicle, comprising: determining a first desired vehicle accelerationbased on a driver command; determining a second desired vehicleacceleration based on a speed control strategy; selecting a maximum ofsaid first desired vehicle acceleration and said second desired vehicleacceleration; and controlling the powertrain so that an actual vehicleacceleration approaches said selected vehicle acceleration.
 2. Themethod recited in claim 1 wherein said second desired vehicleacceleration is determined based on a set vehicle speed and an actualand an actual vehicle speed.
 3. The method recited in claim 2 whereinsaid second desired vehicle acceleration is determined based on adifference between set vehicle speed and actual vehicle speed.
 4. Themethod recited in claim 3 wherein said second desired vehicleacceleration is determined based on said difference and a non-lineargain function.
 5. The method recited in claim 3 wherein said controllingfurther comprises using a first controller when said difference isnegative and using a second controller when said difference is positive.6. The method recited in claim 5 wherein said second controller has asmaller range of authority than said first controller.
 7. The methodrecited in claim 6 wherein said smaller range of authority is providedby limiting a feedback correction quantity.
 8. The method recited inclaim 1 wherein said first desired vehicle acceleration is determinedbased on a driver pedal position and an actual vehicle speed.
 9. Amethod for controlling a powertrain of a vehicle, comprising:determining a first desired vehicle acceleration based on a drivercommand; determining a second desired vehicle acceleration based on aspeed control strategy; comparing said first desired vehicleacceleration to said second desired vehicle acceleration; selecting oneof said first desired vehicle acceleration and said second desiredvehicle acceleration in response to said comparison; determining a firstdesired powertrain torque in response to said selected vehicleacceleration; determining a second desired powertrain torque based on atraction control system; selecting a minimum of said first desiredpowertrain torque and said second desired powertrain torque; andcontrolling the powertrain in response to said selected powertraintorque.
 10. The method recited in claim 9 wherein said second desiredvehicle acceleration is determined based on a set vehicle speed and anactual vehicle speed.
 11. The method recited in claim 10 wherein saidsecond desired vehicle acceleration is determined based on a differencebetween set vehicle speed and actual vehicle speed.
 12. The methodrecited in claim 11 wherein said second desired vehicle acceleration isdetermined based on said difference and a non-linear gain function. 13.The method recited in claim 11 wherein said controlling furthercomprises using a first controller when said difference is negative andusing a second controller when said difference is positive.
 14. Themethod recited in claim 13 wherein said second controller has a smallerrange of authority than said first controller.
 15. The method recited inclaim 14 wherein said smaller range of authority is provided by limitinga feedback correction quantity.
 16. The method recited in claim 9wherein said first desired vehicle acceleration is determined based on adriver pedal position and an actual vehicle speed.
 17. The methodrecited in claim 9 wherein said selecting further comprises selecting amaximum of said first desired vehicle acceleration and said seconddesired vehicle acceleration.
 18. A system for a vehicle having anelectronically controlled drive unit, the system comprising: a firstcontroller that determines a first desired vehicle acceleration based ona driver command, determines a second desired vehicle acceleration basedon a speed control strategy, selects one of said first desired vehicleacceleration and said second desired vehicle acceleration, and adjusts adrive unit operating parameter so that an actual vehicle accelerationapproaches said selected vehicle acceleration; and a second controllerthat determines a preselected acceleration of the vehicle, determines anactual vehicle acceleration based on a sensor coupled to the vehicle,and initiates a reaction when said actual vehicle acceleration isgreater than said preselected acceleration.
 19. The system recited inclaim 18 wherein said preselected acceleration is based on said selectedvehicle acceleration.
 20. The system recited in claim 18 wherein saidfirst controller further adjusts a drive unit torque using a feedforwardterm and a feedback term so that said actual vehicle accelerationapproaches said selected vehicle acceleration.
 21. The system recited inclaim 18 wherein said first controller further adjusts a drive unittorque using a feedforward term and a feedback term so that said actualvehicle acceleration approaches said selected vehicle acceleration,wherein said feedback term is based on a sign of an error between saidactual vehicle acceleration and said selected vehicle acceleration. 22.A method for controlling a powertrain of a vehicle, comprising:determining a first desired vehicle acceleration based on a driver pedalposition and an actual vehicle speed; determining a second desiredvehicle acceleration based on a speed control strategy; selecting one ofsaid first desired vehicle acceleration and said second desired vehicleacceleration; and controlling the powertrain so that an actual vehicleacceleration approaches said selected vehicle acceleration.